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Curiousity Regarding MiG-25 Top Speed

KJ_Lesnick

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I was thinking about something regarding the MiG-25's top-speed. There are some things about it that don't seem to add up...

For example the engines: The Tumansky R-15 -- It only has a pressure ratio of 4.75:1, and 5 compressor-stages and from what I remember a pretty high turbine temperature. I know the Russians didn't quite have the engine capability that we had, but I still find it hard to believe that with that kind of pressure ratio with most of their thrust no doubt coming off ram-compression and the engine's colossal afterburner that it would redline at only Mach 2.83, and burn out at Mach 3.2

The plane had a fuel that had a high-temperature flashpoint, which while not quite as high as the JP-7 used on the Blackbird, still higher than say JP-4. Other than the Blackbird, the only plane I can think of that utilized a high flashpoint fuel was the XB-70 Valkyrie, which used JP-6. It is officially stated to be a Mach 3 capable design, however they did wind-tunnel tests to Mach 4, and the chief-engineer of the project stated that the inlets could perform Mach 4 speed, and it's been acknowledged that the J-93 could achieve it as well.

Now I'm not necessarily saying the MiG-25 could do Mach 4. But I'm wondering if it's limit is 2.8/3.2 or a bit higher than that especially for quick bursts.

Of course I don't know why anyone would lie about it though. It's not like it's a new state of the art design and it's not even our design.


Kendra
 

overscan (PaulMM)

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The engine design was very crude in most respects. It wasn't designed for high turbine entry temperatures, but used low pressure ratio to minimise temperatures. Fuel consumption was high. Above Mach 2.8 it supposedly had problems with overspeeding.

I'm pretty sure there's no hidden "extra performance".
 

KJ_Lesnick

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Overscan,

It doesn't sit right with me. That low a pressure ratio even with Russian-technology of that era to be required to barely achieve Mach 2.83 to Mach 3.20 strikes me as very, very odd.


KJ Lesnick
BTW: The R-15 could could cruise at around Mach 2.4 or Mach 2.5 without afterburner right?
 

sferrin

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KJ_Lesnick said:
Overscan,

It doesn't sit right with me. That low a pressure ratio even with Russian-technology of that era to be required to barely achieve Mach 2.83 to Mach 3.20 strikes me as very, very odd.


You need to consider it in context. If the ram effect of speed and the intake is already compressing it by (for example only) 7 and then the engine has a 5 to 1 pressure ratio, the effective compression ratio is 35 to 1.





KJ Lesnick
BTW: The R-15 could could cruise at around Mach 2.4 or Mach 2.5 without afterburner right?


[/quote]
 

sferrin

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KJ_Lesnick said:
BTW: The R-15 could could cruise at around Mach 2.4 or Mach 2.5 without afterburner right?

Where did you get this? ::)
 
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that Syrian Mig-25 definitely had its engines destroyed and it flew at Mach 3.3
Indian Mig-25Rs have clocked close to Mach 3 but this was only through special permit by the prime Minister's Office! (overflights, only)
we had only 8 Mig-25R's and 4 U's , couldn't afford engine losses . they mostly flew at <= Mach 2.5 on the higher end of things. Maintenance was always brutal.
 

r16

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the Mig-25 is a known identity , it could "probably" be doing more but it is also a weapon system and the demands arising from that limit it to Mach 2,8 / 3.2 . The same requirements to engage high speed targets led to '31 being slower as it is easier driving a missile .

if ı remember it right ,the engine was developed for a drone and for that application it could really cruise at that kind of speeds as the drag of the airframe it was on would not require afterburning.
 

KJ_Lesnick

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sferrin said:
Where in the world did you get this? ::)

On an aviation forum. It was a good website: There were a number of members that included pilots, mechanics (Both military and civilian) and aerospace engineers. This piece of information came up during a discussion about the MiG-25 and it's engines. Being that even before that I've heard information of the MiG-25 being able to cruise super-sonically, (without afterburner) and actually having a higher supersonic combat radius than a subsonic one. (which actually partially played a role in Lt. Belenko landing on fumes in Japan) I see no reason to believe the information mentioned was inaccurate.


avatar said:
that Syrian Mig-25 definitely had its engines destroyed and it flew at Mach 3.3

Who said it reached Mach 3.3?

r16 said:
if ı remember it right ,the engine was developed for a drone and for that application it could really cruise at that kind of speeds as the drag of the airframe it was on would not require afterburning.

Actually... that might not entirely be true!

I've heard conflicting sources on this one, of which one said it was for a drone, but another said it was originally for a MiG testbed, but none of the planes could actually achieve the speed the engine was designed to routinely operate at. The engine then LATER ended up being used in some kind of high-speed cruise-missile.


Kendra Lesnick
 

sferrin

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KJ_Lesnick said:
sferrin said:
Where in the world did you get this? ::)

On an aviation forum.

Oh, well, then it must be true. ::)



KJ_Lesnick said:
It was a good website: There were a number of members that included pilots, mechanics (Both military and civilian) and aerospace engineers. This piece of information came up during a discussion about the MiG-25 and it's engines. Being that even before that I've heard information of the MiG-25 being able to cruise super-sonically, (without afterburner)

Interesting that nobody else has heard that story. (Which is incorrect BTW. Sounds like the ravings of a fanboy.)



KJ_Lesnick said:
I see no reason to believe the information mentioned was inaccurate.

Well how about because there are no documented sources that support it for starters? You sound fairly new to internet forums as you seem to be extraordinarily trusting. ("Gullible" crossed my mind but that might be a bit harsh.)
 

KJ_Lesnick

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sferrin said:
Oh, well, then it must be true. ::)

Sure it could be wrong. But I've been on the net a little bit longer than you guys give me credit for. Many of the people I talked to had a lot of experience under their belt and knew their stuff.


Interesting that nobody else has heard that story. (Which is incorrect BTW. Sounds like the ravings of a fanboy.)

Which part was incorrect?


Well how about because there are no documented sources that support it for starters? You sound fairly new to internet forums as you seem to be extraordinarily trusting. ("Gullible" crossed my mind but that might be a bit harsh.)

I've been online a little bit longer than you think. Plus these individuals in the past have been reliable when it came to sources of information generally.
 
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ok Kendra
you win its Mach 3.2 not mach 3.3 :p
The Americans had clocked a Mig-25 over Israel at Mach 3.2 in 1973. Upon landing in Egypt, the engines were totally destroyed.

http://www.geocities.com/siafdu/foxbat2.html
http://www.aerospaceweb.org/question/performance/q0239.shtml
http://www.wvi.com/~sr71webmaster/mig25.html
http://www.battle-fleet.com/pw/his/MIG25_Russian_Interceptor_Foxbat.htm
http://en.wikipedia.org/wiki/MiG-25
 

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According to 'Slava', former Foxbat pilot at http://www.forumavia.ru/forum/3/4/799342141873030972351059041734_1.shtml?topiccount=42, Mig-25 could go 3100-3200 km/h instrumental speed (M=3), with Flight Manual restriction to M=2,83, but this was undesirable result of rapid thrust increase after reaching speeds over M=2.6-2.7 and pilot's being 'captivated'. Airframe was not a limiting factor in his words ('untill airframe starts to corrugate', 'but I'm not an engineer' he states). He don't know cases of engines being replaced after going 'beyond M=3', 'if there were no overheating'). Problem was to stop acceleration (you just can't easily turn off forsage at this speed) correctly, moving throttle not below Military Power (rule used for all speed above M=2.2). Flight manual flight envelope chart shows, meanwhile, strong vertical line just after M=3.0 - 'Wing Divergence'.
 
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the bursts over Israel were precisely that "bursts" // so even for a quick dash I think the speed was pretty much Mach 3.2 before the engine got destroyed
 

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An engine for fast, high-altitude MiG-25 aircraft. They were developed in the 1960s.

R-15

AMNTK Soyuz (Tumansky), Russia (development)
OKB of A. A. Mikulin, Russia (development)
MMPP Salyut, Russia (production)

The single-shaft R-15 engine was developed specially for flight at high altitude and at a speed exceeding M=2.5. The basic variant of the engine was designed by OKB-300 of S. K. Tumansky, further development was continued in cooperation with OKB of A. A. Mikulin. Initially, it was intended for use with the strategic nuclear cruising missile Tu-121 with a range of almost 4000 km. This missile was first launched in August 1959, but next year the project was abandoned, because the main interest was shifted to ballistic missiles. Specially for this type of devices, the 15K propulsion plant (also referred to as R-15K-300 or KR-15-300) with afterburner thrust of 10000 kp was developed. The first engines produced in series were mounted into “giant” reconnaissance drones Tu-123 Jastreb (DBR-2). These originated by a modification of the Tu-121 missiles in 1960-61, were deployed on 23rd May 1964 and 52 of them had been produced until 1972. Regarding the thermodynamic processes, the R-15 was close to scramjets. This was corresponded by the supercharger outlet pressure, which was under static conditions very low even for that time period. The supercharger compression was compensated by scramjet compression and by a special uncontrollable nozzle. Because of this, the thrust at high altitudes and speeds of about M=2.5 was significantly higher than the one of usual engines – it was close to 20 tons (almost 200 kN). Long lifetime was not expected, and the guaranteed service time without failure was determined to be only 50 hours. When related to the Tu-121 missile, the guaranteed service time is sometimes stated at only 15 hours, while the engine was able to run continually on full afterburner for 3 hours.

In 1957, a prototype of the E-150 fighter plane was designed on drawing boards. The use of the previous engines, modified and designated as R-15-300(M), was planned. It took 18 months to finish the engines, and the first E-150 prototype did not take off until 8th July 1960. Beginning in 1962, the second E-150 prototype tested the upgraded R-15M-300 engines with improved high-altitude performance. The direct successor of the E-150, the E-152, was flown since 21st May 1961, also with one R-15-300(M) engine (attention, the E-152A had two R-11F-300 engines). In the FAI system, the plane was referred to as E-166, and the engine as R-166. The lifetime already became a difficulty – service time of only several dozen hours only sufficed for ground tests and trial flights, but for mass-produced aircraft, the engine had to be tuned up and much more reliable. Even though, the R-15-300 engines and modifications collected on the E-150, E-152 and E-152M planes a significant amount of flying hours, including flights at high altitudes and at high speeds. The E-151, the armed variant of the E-150 driven by the same engine, was only built as a mockup.

The R-15, as the only available engine with the required parameters, was chosen for propulsion of the E-155, the MiG-25 prototype. To tell the truth, it was not the only engine of this performance level. The Rybinsk design bureau led by P. A. Kolesov designed and tested even more powerful RD17-16 engines at the same time. However, only a handful of these engines were built, and it was assigned for use with the M-52 supersonic bomber, which, in the end, has never flown. Lyulka also worked on an engine of the same thrust class, but the project was only on the drawing board at that time.

For the use with the E-155 aircraft, the R-15B-300 (Izdeliye 15B) variant was developed, with a number of design changes in comparison to the original 15K engines from the drones and the R-15-300 engines from the test planes. In a short time, the designers performed a replacement of the original simple hydromechanic fuel intake control system, optimized for operation at a constant thrust, by a fully governable electronic system (for the first time on a Soviet combat aircraft), type RRD-15B with a spare mechanic system. The work on the electronic governor was led by S. Chiekunov. The problem of the original hydromechanic control became evident already with the E-150 and E-152 planes, where the fuel flow rate was often being changed in a wide range of 150 – 15000 kg per hour. The system was not designed for so different flow rates. For the E-155, the accuracy of RPM control of 0.2 % was required, and furthermore, the system had to be bound with air inlet governor.

The afterburner chamber was the biggest one that has been built by that time. Furthermore, a new, three-position nozzle had to be designed. The five-stage supercharger was also modified, less tending to **** (pumpaz – don’t know what it is, sorry - Utchoud), and the tube-annular combustion chamber, now working at a 50°C higher temperature was tuned for operation at a higher altitude. The turbine has one stage. The special T-6 (T – Toplivo) kerosene with high boiling point is used as fuel. The fuel can be replaced by T-7P and RT (Reaktivnoye Toplivo). Each engine has its own fire detector with ionization sensors and a chlorine-fluorine-carbon (CFC) extinguisher. The RPM at maximum power were 7000.

(Image)

The rear edge of the engine has a respectable diameter of almost 150 cm

The final version of the R-15B-300 and especially its electronic control system was tested intensively in 1963-64 under the Tu-16LL flying laboratory first. The results, however, did not provide all the necessary information, because the flight conditions offered by the T-16 plane were far of those the engine was optimized for. The first R-15B-300 only had a lifetime of 25 hours! The E-155 took off for the first time in March 1964, and in 1965-75 the planes of this type established 21 world records. In the FAI system, the plane was referred to as E-266 and the engine as R-266, that everything in order to confuse the “western” enemy. The lifetime of the engines of the first serial MiG-25 aircraft was designated as 150 hours, for the following series it was increased to 750 hours of operation. Continuous afterburner operation was initially set to 3 minutes. Later it was increased to 8 and then to 40 minutes. The nozzles are in their rear parts turned slightly toward each other due to aerodynamic purposes, and are so close to each other that their profiles blend together. Therefore, 3 segments had to be removed from each nozzle and replaced by a separating block, attached onto the fuselage. Because of significant heating of the engine surfaces, the aircraft had to be equipped with a high-quality thermal shielding. The engines were used on older MiG-25 aircraft and they proved to be sufficiently reliable even under demanding climate conditions ranging from cold Russia to hot Egypt. The designers of the MiG-25 were finally awarded the Lenin prize, and Fedor Shukhov got it for the R-15B-300 propulsion plant.

The unsuccessful T-37 aircraft project was also based on these engines. The twin-engined Tu-128 2R-15B-300 interceptor, as well as the four-engined Tu-125 supersonic bomber, also remained in the project stage.

(Image)

Engine mounting and placement of fuel tanks with a capacity of 15 tons of special kerosene in the MiG-25 aircraft.

However, the R-15B-300 engines always restricted the MiG-25 performance (cruise speed, range, ...). In flight above M=2.8 they had a tendency to uncontrollable over-revving, they overheated and could have caught fire. After M=3.2 flights (e.g. over Israel at that time) they had to be replaced. Soon after the MiG-25 was deployed, more powerful and more economical propulsion plants were demanded. This could have been achieved even by a not very drastic change of the already available engines.

The new R-15BF2-300 (Izdeliye 65M) by Shukhov and Rotmistrov designers had one more supercharger stage added, and new materials used in the combustion chamber and in the turbine allowed operation at higher temperature. While the outer dimensions were maintained, the compression ratio was increased from 4.75 to 4.95, and fuel consumption was lowered. Thrust increased by about a quarter and would have allowed flights at 3500 kph. Since 1973, the engines were tested on two E-155M (MiG-25M) planes, which achieved several records in climb rate and ceiling. Although the increase of aircraft performance was proved and the engines were fully exchangeable with the previous versions, the serial production of the R-15, lasting for over 10 years, would have been unnecessarily complicated. However, the main issue was that the USSR began changing priorities at that time and extreme speed was no longer as important as before. Furthermore, Koliesov’s PS-30F (D-30F) engines for the planned MiG-31 offered similar performance, but had significantly lower fuel consumption.

The last version produced in series was the R-15BD-300 with modified equipment (gearbox, ...), lifetime designated to be 1000 hours and with “equal” performance as its predecessor (see the note below the chart of technical data). The engine was mounted to new series of MiG-25 beginning in the late 1970s, namely at least to these versions: PD, BM and conversions of older aircraft to the versions PDS and RBF. The older MiG-25 planes, whose engines had reached the end of their service time, were already becoming the new R-15BD-300 engines. The later series of the R-15BD-300 had a slightly higher thrust.

One more engine variant was to originate, the R-15BV-300 (V – Vysotnyj), with improved power at high altitudes. The engine would have allowed flight at unprecedented speed of M=3.5 (over 3700 kph). In the mid 1960s, the engine was considered in conjunction with the E-155PA (MiG-25PA) interceptor. However, the project was not continued any further.

Table:

Type
Length (mm)
Intake diameter (mm)
Maximum diameter (mm)
Dry weight (kg)
Overall compression
Maximum temperature in front of the turbine (°C)
Maximum temperature behind the turbine (°C) - 820 (in flight), 800 (start-ups)
Maximum thrust (kp)
- with afterburner (kp)
- afterburner alt=15 km, M=1.8
- afterburner alt=11 km, M=2.4
Specific fuel consumption – maximum (kg/kp/h)
- with afterburner (kg/kp/h)

Unless specified, thrust and fuel consumption are at alt=0, M=0.

KJ, note that the engine was developed for the Tu-121 strategic cruise missile. A derivative was used on the MiG Ye-150 but it wasn't very successful - the R-15K was designed for constant thrust at high altitude and low life, which wasn't appropriate for fighter. This resulted in a redesign to the R-15B-300 for the MiG-25.
 

KJ_Lesnick

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avatar said:
The Americans had clocked a Mig-25 over Israel at Mach 3.2 in 1973. Upon landing in Egypt, the engines were totally destroyed.

Compelling information. Unfortunately, the speed listed is what we are TOLD was observed. I've also heard other claims of MiG-25's doing 3.4 Mach during possibly the same overflight, or during another Israel overflight.

Not to sound distrusting, but keep in mind what a person is told isn't always what's true. After all, the Blackbird's speed has never been declassified and many people still accept the figure that the plane can do Mach 3.2, maybe 3.6 tops (even despite the fact that the Blackbird uses a specific type of Titanium alloy that can go up to 1,200 C, is actively cooled and the J-58 without any mods can do Mach 4 -- not even requring a bleed-bypass system, engine-trim and derich, active cooling for the engine, metallurgy changes and extra air-cooling.)


Kendra Lesnick
 

sferrin

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KJ_Lesnick said:
avatar said:
The Americans had clocked a Mig-25 over Israel at Mach 3.2 in 1973. Upon landing in Egypt, the engines were totally destroyed.

Compelling information. Unfortunately, the speed listed is what we are TOLD was observed. I've also heard other claims of MiG-25's doing 3.4 Mach during possibly the same overflight, or during another Israel overflight.

Not to sound distrusting, but keep in mind what a person is told isn't always what's true. [/i]


Kendra Lesnick

So basically, if it's what you want to hear you believe it even if it's just on a forum but if it doesn't agree with what you want to hear you distrust it no matter that it's been cited hundreds of times over the years in numerous reputable publications? I believe there's a name for that. ::)
 

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overscan said:
These originated by a modification of the Tu-121 missiles in 1960-61, were deployed on 23rd May 1964 and 52 of them had been produced until 1972. Regarding the thermodynamic processes, the R-15 was close to scramjets. This was corresponded by the supercharger outlet pressure, which was under static conditions very low even for that time period. The supercharger compression was compensated by scramjet compression and by a special uncontrollable nozzle. Because of this, the thrust at high altitudes and speeds of about M=2.5 was significantly higher than the one of usual engines – it was close to 20 tons (almost 200 kN). Long lifetime was not expected, and the guaranteed service time without failure was determined to be only 50 hours. When related to the Tu-121 missile, the guaranteed service time is sometimes stated at only 15 hours, while the engine was able to run continually on full afterburner for 3 hours.

Huh? How did it work like a scramjet? And what's a supercharger-outlet pressure? And each engine produced 40,000 pounds of thrust at altitude at Mach 2.5?

Emphasis mine on the bold parts


Kendra Lesnick
BTW: Regarding the R-15BF2-300 and R-15BV-300 which were developed in the mid 1960's and not fitted to any production MiG-25 -- did the US know of these developments during the MiG-25 development? Or were they unaware of it?
 
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okay .. Let's say the American radar operators deliberately understated the speed . Let's say it was Mach 3.4 and not Mach 3.2. if you agree that the engines were destroyed , then at least these engines were susceptible beyond Mach 3.something.

Track-2 even if the Mach 3.2 is an urban legend, we do have the assertions by Indian Airforce pilots, at the time of Mig-25R retirement in 2006.

Track-3 even if that is a fabrication, why would the Americans at the peak of the cold war understate the max "tenable" speed of the fearsome foxbat? I say this because they made a point about the MIg-25s engines being destroyed.
 

KJ_Lesnick

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sferrin said:
So basically, if it's what you want to hear you believe it even if it's just on a forum but if it doesn't agree with what you want to hear you distrust it no matter that it's been cited hundreds of times over the years in numerous reputable publications? I believe there's a name for that. ::)

That's not what I was saying. I was saying considering the high temperature structure of the plane, it's low volatility fuel, and the engine's low-pressure ratio (not to mention it's large nozzles and gigantic afterburner) point to a higher speed than Mach 2.8 to Mach 3.2 max (consider that a J-75 can at least equal Mach 3) even considering Russian designs were known to be kind of crappy.

And there have been many cases where information was repeatedly reported as truth when later on we'd find out that it wasn't entirely accurate even misinformation. I think the buildup to the Iraq war was kind of based on this. I would be looked at far wackier and worse if I, prior to the invasion of Iraq, said that there were no WMD's there and Bush, Cheney, the CIA and all of 'em were basically fabricating information and deliberately listening to sources they knew were unreliable but helped make their case to furnish evidence which would be use to trick Congress, and the American people into believing Iraq was a major threat, and was partially responsible for 9/11 to achive war with Iraq -- in fact with the patriotic fervor at the time I'd probably be viewed as a traitor of some sort. Yet what I said is completely true.

Quite a more extreme example though
 
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don't hate me for sounding like trying to moderate ( or the lack of it) let's stick to the topic and leave this my source versus your source business .
Let's continue as we started
discussing on :
1. Technical feasibility
2. Cold war logicality
 

KJ_Lesnick

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avatar said:
okay .. Let's say the American radar operators deliberately understated the speed . Let's say it was Mach 3.4 and not Mach 3.2. if you agree that the engines were destroyed , then at least these engines were susceptible beyond Mach 3.something.

Well considering that old Soviet high-performance engines are not known for the longevity that Western counterparts are known for, it seems to make sense that after five minutes with the throttles slammed to 120% RPM due to a fuel-control malfunction that the engine would be a wreck. Obviously the engines were succeptable to this problem at the upper end of the plane's performance envelope.


Track-2 even if the Mach 3.2 is an urban legend, we do have the assertions by Indian Airforce pilots, at the time of Mig-25R retirement in 2006.

I would not be suprized there would be assertions by Indian Air Force pilots of a Mach 3.2 capability whether accurate or understated. Not to sound stubborn but SR-71 pilots often asserted they flew at Mach 3.2, with Mach 3.5 mentioned at the top. However despite this there is ample evidence to suggest the Blackbird is way faster than that.


Track-3 even if that is a fabrication, why would the Americans at the peak of the cold war understate the max "tenable" speed of the fearsome foxbat? I say this because they made a point about the MIg-25s engines being destroyed.

My guess would be that the USAF was not fond of admitting the F-15 could do whatever the MiG-25 could do in terms of top-speed. The F-15 even after the cold-war ended was still a front-line fighter and I guess they didn't want to reveal the speed of one figuring it might reveal the speed of the other. (Hope I don't get a heart-attack or disappear :eek: )


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overscan (PaulMM)

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F-15 top speed really isn't as high as the MiG-25. Mach 2.5 was demonstrated briefly on the F-15 but wasn't operational practice.
Even the MiG-25 tended to operate at Mach 2.35, a speed it could sustain for long periods, rather than Mach 2.5-Mach 2.8.

I suggest you investigate the effect of 25:1+ compression ratio and turbofan bypass ratios on Mach 2+ thrust. F100 wasn't a high speed optimised design.
 

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KJ_Lesnick said:
overscan said:
These originated by a modification of the Tu-121 missiles in 1960-61, were deployed on 23rd May 1964 and 52 of them had been produced until 1972. Regarding the thermodynamic processes, the R-15 was close to scramjets. This was corresponded by the supercharger outlet pressure, which was under static conditions very low even for that time period. The supercharger compression was compensated by scramjet compression and by a special uncontrollable nozzle. Because of this, the thrust at high altitudes and speeds of about M=2.5 was significantly higher than the one of usual engines – it was close to 20 tons (almost 200 kN). Long lifetime was not expected, and the guaranteed service time without failure was determined to be only 50 hours. When related to the Tu-121 missile, the guaranteed service time is sometimes stated at only 15 hours, while the engine was able to run continually on full afterburner for 3 hours.

Huh? How did it work like a scramjet? And what's a supercharger-outlet pressure? And each engine produced 40,000 pounds of thrust at altitude at Mach 2.5?

I guess the author means it had partially supersonic air flow through the compressor. The article was translated from Russian and isn't completely clear.

KJ_Lesnick said:
Kendra Lesnick
BTW: Regarding the R-15BF2-300 and R-15BV-300 which were developed in the mid 1960's and not fitted to any production MiG-25 -- did the US know of these developments during the MiG-25 development? Or were they unaware of it?
Given that publicly at least the engines were long referred to as "R-31", not R-15, Western knowledge of the engines in the MiG-25 seems to have been limited.
 

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http://www.mzak.cz/motory/r-15/ has lots of technical info, including charts that seem to be from the MiG-25 flight manual.
 

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f-15 was preferred by Pentagon to dogfight subsonically at a higher speed than was the norm , hence the fixed leading edge with camber . High speed target interception is not what it is aiming at .It is not what Mig-25 is . After the 1967 scare USAF spent lots of time to check whether the Russians were "fast" .It turned out they were not . It was only for insurance that the original McDD design that relied on F-16 like fuselage wing transformation was changed into the present form ; which then needed fast packs to get the original fuel tankage .

ı personally believe the reconnaisance flights over Israel is underrated by the west , though the pilot must have been most careful to fly at Mach 3.2 .In the unlikely event the Mig is cleared for even higher speeds , the pilot would still fly at that speed because it is also a political statement .It would look bad on the part of the Mig Driver to run like a rabbit . He would have to fly a predictable and immaculate pattern . Mach 3.4 is most unlikely .
 

KJ_Lesnick

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overscan said:
F-15 top speed really isn't as high as the MiG-25. Mach 2.5 was demonstrated briefly on the F-15 but wasn't operational practice.
Even the MiG-25 tended to operate at Mach 2.35, a speed it could sustain for long periods, rather than Mach 2.5-Mach 2.8.

Actually, even the USAF has so far admitted to the F-15's operational limit being around 1,850 miles an hour. I also had a calendar two years ago which had pictures of USAF (possibly some USN) fighters as well and even the F-15E was listed as having Mach 2.8 performance. It was also stated that with the carrying of (not sure) either 4 x AIM-7 or 4 x AIM-120 in a flush-mounts the drag increase was so low as to consider the plane flying clean.

If these figures are the true F-15's capabilities, a speed of Mach 2.5 is well within it's operating limit.

I suggest you investigate the effect of 25:1+ compression ratio and turbofan bypass ratios on Mach 2+ thrust. F100 wasn't a high speed optimised design.

The Soloviev D-30F6 can go pretty fast and it's pressure ratio ain't terrible either.


overscan said:
I guess the author means it had partially supersonic air flow through the compressor. The article was translated from Russian and isn't completely clear.

I guess not everything translates exactly the same. While supersonic flow routinely occurs on the tips of high-bypass turbofan blade-tips at high RPM's, that doesn't sound all that good to have partially supersonic flow throughout the compressor? Am I wrong?


Given that publicly at least the engines were long referred to as "R-31", not R-15, Western knowledge of the engines in the MiG-25 seems to have been limited.
[/quote]

Good point.


overscan said:
http://www.mzak.cz/motory/r-15/ has lots of technical info, including charts that seem to be from the MiG-25 flight manual.

Thanks


r16 said:
f-15 was preferred by Pentagon to dogfight subsonically at a higher speed than was the norm , hence the fixed leading edge with camber . High speed target interception is not what it is aiming at .It is not what Mig-25 is . After the 1967 scare USAF spent lots of time to check whether the Russians were "fast" .It turned out they were not . It was only for insurance that the original McDD design that relied on F-16 like fuselage wing transformation was changed into the present form ; which then needed fast packs to get the original fuel tankage .

I know of the dog-fighting requirement. I don't know why there was such a scare about the MiG-25 -- it was blatently obvious that the plane was designed as an interceptor and was not an air superiority fighter. But nonetheless they designed the plane with the capabilities of catching the MiG-25.

By the way, do you have any picture of that Chined F-15 design you're talking about -- sounds like it would look slick.


Kendra Lesnick
 

overscan (PaulMM)

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You have a fair point but the D-30F6 was specifically designed for high speeds. I would imagine it uses some form of bypass system to divert air from the core to the outer duct and turn it more into a ramjet as speeds increase. The French were looking at doing this with their TF30 derivative, the TF306, for Mach 3 flight, in the late 1960s.

I've always wondered about the MiG-31's engine design actually.
 

overscan (PaulMM)

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KJ_Lesnick said:
I also had a calendar two years ago which had pictures of USAF (possibly some USN) fighters as well and even the F-15E was listed as having Mach 2.8 performance. It was also stated that with the carrying of (not sure) either 4 x AIM-7 or 4 x AIM-120 in a flush-mounts the drag increase was so low as to consider the plane flying clean.

KJ, I can't believe you just cited a calendar as a source.

Please use some common sense when evaluating the trustworthiness of sources. Topps Trumps cards or calendars don't rate very highly.
 

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the only place I certainly remember that the original F-15 was mentioned is the Bill Gunston / Mike Spick book the Modern Air Combat , though it may also been posted in this forum .

the Mig scare is due to the 6 day war of 1967 . As the Arab defeat made no impression on the Russians and this was very quickly noted by Western intelligence the reasoning was there was something not yet noticed . And the Domedovo event came at the end of the month and the Russians showed their new toys with the Foxbat being listed as the Mig-23 .Since it was known the early number was slated for the Frontal Aviation there was much confusion . But it was over by end of the year and the next two years there were serious work instead of so called "panic" .

ı believe your quotes of speed for F-15s are unachieveable by the run of the mill Eagles . Unless USAF had special and undeclared versions they are too high . Maybe they did and forgot them in the Nevada Desert to prevent them being a threat to the supercruising F-22 , this was jokingly reported in this forum as a USN magazine declaring the plane buried in the sand but I wouldn't give much credit to that.

on the other forums You are in , maybe they are spreading misinformation , though this doesn't definitely mean that they are wrong in doing that . Being once blamed for protecting Nazis , I have first hand experience that web is some sort of a battlefield .
 

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overscan said:
KJ_Lesnick said:
I also had a calendar two years ago which had pictures of USAF (possibly some USN) fighters as well and even the F-15E was listed as having Mach 2.8 performance. It was also stated that with the carrying of (not sure) either 4 x AIM-7 or 4 x AIM-120 in a flush-mounts the drag increase was so low as to consider the plane flying clean.

KJ, I can't believe you just cited a calendar as a source.

Please use some common sense when evaluating the trustworthiness of sources. Topps Trumps cards or calendars don't rate very highly.

:D

X 50. We all have brains, we should be using them when evaluating the accuracy of claims we hear. I had an F-16 maintainer tell me the U-2 could go Mach 3. Some here would say "well he's in the USAF so it MUST be true" while others would recognize it for the mistake it was (he obviously meant the Blackbird). Simply parroting a figure seen somewhere because it supports ones wishes doesn't reflect very highly on the poster and has the effect of dragging down the overall quality of the site when it is inundated with this type of unsubstantiated BS from certain quarters.
 

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overscan said:
You have a fair point but the D-30F6 was specifically designed for high speeds. I would imagine it uses some form of bypass system to divert air from the core to the outer duct and turn it more into a ramjet as speeds increase. The French were looking at doing this with their TF30 derivative, the TF306, for Mach 3 flight, in the late 1960s.

I've always wondered about the MiG-31's engine design actually.
[/quote]

Regarding the MiG-31's design, I remember seeing in a book about jet-engines which showed the engine-design. It looked like an relatively small afterburning turbofan compared to it's gigantic afterburner. It didn't feature any bleed-bypass -- just a fan.

Regarding the French TF-306 Turboramjet, I never knew the French were planning on fitting a TF-30 with a bleed-bypass. What plane was it being designed for?


KJ, I can't believe you just cited a calendar as a source.

Well, it's not like it was *only* mentioned in the calendar! I read in other sources, which were a bit more reliable than a calender similar claims -- around 1,850 mph (I mentioned the calendar because it showed the same figure and is obviously public knowledge)


r16 said:
the only place I certainly remember that the original F-15 was mentioned is the Bill Gunston / Mike Spick book the Modern Air Combat , though it may also been posted in this forum .

the Mig scare is due to the 6 day war of 1967 . As the Arab defeat made no impression on the Russians and this was very quickly noted by Western intelligence the reasoning was there was something not yet noticed . And the Domedovo event came at the end of the month and the Russians showed their new toys with the Foxbat being listed as the Mig-23 .Since it was known the early number was slated for the Frontal Aviation there was much confusion . But it was over by end of the year and the next two years there were serious work instead of so called "panic" .

If correct, you're saying they mixed up the MiG-25 with the MiG-23 (which was known as an air superiority fighter). Was there suspicion about another interceptor being developed by the Russians, or did they think they were somehow one and the same?


on the other forums You are in , maybe they are spreading misinformation , though this doesn't definitely mean that they are wrong in doing that . Being once blamed for protecting Nazis , I have first hand experience that web is some sort of a battlefield .

I suppose misinformation is a possibility. But I remember reading other stuff about F-15's being used in a simulated excercize to see how well they would do shooting down an SR-71 because of it's performance being similar to a MiG-25.


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Topic is locked. There is too much speculation and not enough hard facts in this discussion. This is a conversation better suited to ATS forum, email or msn messenger than this forum.
 

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Just a few facts and little speculation at the end:

D-30F6s design is actually nothing special - low bypass ratio, construction scheme is 5/10/2/2 (LPC/HPC/HPT/LPT), huge afterburner and no extra features like bypass ducts from J58. Little more info is here http://www.mzak.cz/motory/d-30f6/. Only in Czech language at this time, will be translated.

You also might be interested in this comparision of R-15B-300 and AL-31F (from Su-27) http://www.mzak.cz/teorie/pics/vr_char.gif being related to speed characteristics of both engines. You can clearly see that R-15B-300 is optimised for high speed flights where thrust-to-weight ratio at this speed is almost the same for both engines. The time gap between both engines is about 20 years.

Some facts about SR-71 might be useful in this thread. Maximal operational speed is M=3,2 with possibility to go to 3,3 when authorised by commander. Official speed record is about 3,4 I think. This source http://maggiesfarm.anotherdotcom.com/archives/7821-Major-Brian-Shul-I-loved-that-jet.html says it can reach at least 3,5. J58 engines were tested on ground bench, which could simulate speeds up to M=3,7.

Flight manual of MiG-25RB allows only 5 minuts of operational flight on speed M=2,65 to 2,83. The second number is also maximal allowed operational airspeed (H>18km). The limiting factor is surface temperature, which can't exceed 290°C. From limiting splines tendencies in manual's flight envelopes I guess the maximal speed given by engines power and structural limits and not taking the surface temperature in account is somewhere slightly over M=3. I belive MiG-25 can no way go over 3,1 or maybe 3,15, maybe little bit more in good conditions. I guess the design of inlet duct is not as effective as on SR-71 and produces much less thrust when operating on M=~3 compared with SR-71. 58% of total SR-71 thrust is generated in inlet at speeds about M=3,2.
 

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